8 ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



THE AIM AND SCOPE OF THE PRESENT RESEARCH. 



The preceding review outlines the present theory of amalgam cells. No part 

 of this theory has yet been verified with the precision that our present knowl- 

 edge of absolute units would justify. The exactness of the equation of 

 Cady is still somewhat in doubt, and Haber's considerations as yet lack 

 adequate experimental support. Far more pressing is a proof of the pre- 

 cision of the gas law at infinite dilution. This law is a cornerstone of 

 modern thermodynamics, but its exact truth is inferred more from extra- 

 polation and analogy than from experimental data. These and minor con- 

 siderations prompted the inception of the present research. 



To solve these problems at all completely, the electrical measurement 

 should be accurate to one hundred thousandth of a volt, and the calorimetric 

 determinations of the heats of dilution precise to an equivalent degree. With 

 such data at hand a distinct advance can be made. 



There seems to be no reason why the potential of a given concentration 

 of liquid amalgam at constant temperature should not be perfectly definite 

 when all secondary effects are excluded. On the other hand, most solids, by 

 reason of their variable surface energy, do not give very sharply defined 

 potentials, and so do not come within the province of this research. 



Sodium amalgams, though striking in their peculiarities, are hard to pre- 

 pare in a state of unquestionable purity, and they react vigorously with 

 aqueous solutions. Unpublished work by Richards and Lewis in 1899 failed 

 to reveal any inert electrolyte for use in the cell. The method of Renter, 28 

 who used alcoholic solutions at 8o, is impracticable for accurate work. 

 Hence, zinc and cadmium amalgams, which appear open to neither of these 

 objections, are selected as best adapted to the requirements of the research. 

 It is true that preliminary experiments by the method of Richards and Lewis 

 seemed to indicate a slight reaction with aqueous sulphate solutions, even 

 when these had previously stood in contact with another sample of amalgam. 

 But this effect was finally referred to oxidation and carefully eliminated in 

 a manner soon to be described. 



"Chem. Cent. Blatt, 73, II, 1290 (1902). 



/ 





